This invention relates to a sensor system for in-situ monitoring of lubricant oil quality and to a method of monitoring the lubricant oil quality in-situ. More specifically, the invention relates to a microprocessor controlled solid-state monitor of lubricant oil quality for use especially in automotive, as well as other motive applications.
Lubricant oil in use in automotive applications or other combustion engine applications is subjected to an aging process as a result of its use in the engine operation. The exposure of oil to high temperature zones in the presence of NO.sub.x, moisture and air are main factors contributing to chemical changes which decrease the oils' lubricating effectiveness.
As a result of this decrease in its effectiveness, detrimental effects may result on the engine parts, for example, accelerated corrosion. As a further aspect of its use in a lubricant environment in automotive engines, corrosivity of lubricant oil increases with use due to the oil degradation as well as a break up of the protective additives therein. The extent of oil degradation and break up of protective additives depends on various factors such as base oil formulation, type and amount of protective additives, engine design and vehicle operating conditions. Accordingly, the customary change of oil at regular intervals of time or mileage does not necessarily provide adequate protection for engine parts because the mileage alone is not a sufficient indication of the oil quality. More specifically, the oil, depending on the type of use may be changed either too soon, causing an unnecessary cost in oil and labor expended, or too late, contributing to damage of engine parts.
Moreover, even though the effectiveness of lubricant oil, when sold, has to meet industry established standards, oil formulations can and do vary greatly from one oil manufacturer to another. More specifically, every oil contains a number of additives which vary greatly in both quality and quantity from one manufacturer to another. The oil origin can be paraffinic, synthetic, or a mixture of both and will also vary in accordance to the refining processes employed to manufacture the oil. With respect to additives, they typically amount to 5% to 25% of a base oil and will be made up of, for example, anti-oxidants (S, N, Se, As, Zn--containing organics, phenol derivatives, chelating agents, etc.), viscosity index improvers (linear polymers such as polyolefins and the like), detergents and dispersants, friction modifiers "anti-squawk" and "anti-chatter" agents such as fatty acid esters, alcohols and amines, anti-wear agents, anti-foam agents (liquid silicone, polyethelene glycol ethers and sulfides), corrosion inhibitors/meta passivators (N-compounds, fatty acid amides, carboxylic acid derivative), and others such as preservatives, odorants and the like.
As oil ages, degradation products of various type accumulate. Moreover, accumulation of other contaminants will occur simultaneously, including mineral acids such as sulfur, nitrogen and hydrohalic based acids, soot and water. The final result is an oil whose acidity, corrosivity and viscosity has substantially increased as it reaches the end of its useful life, which as previously indicated, can result in disastrous consequences when continued in use in an internal combustion engine.
Up to now, there has been no system or method of measuring the deterioration of oil in-situ in an automotive environment. Current practices of determining oil condiion require laboratory measurements such as titration of total base numbers, i.e., TBN, which is defined as the number of miligrams of KOH required to neutralize all acidic constituents present in one gram of a sample of oil. Change in viscosity of oil is not considered to be a practical indicator of oil conditions since it varies with temperature.
The degree of additive degradation on the other hand would be a good measure of oil condition. A problem with this is that each oil contains different additives so that different sensing devices would have to be designed for different oils. At the same time, other physical properties of oil such as fluoresence, specific gravity, color, dielectric constant, interfacial tension and the like could, in principle, be used for quality control tests. However, all of these tests must necessarily be performed in a laboratory environment.
In accordance with the invention, the problem of having to conduct oil testing in a laboratory environment is thus avoided.